Chronic allograft vasculopathy (CAV), or graft arterial lumen occlusion through intinna expansion, is a major cause of late heart transplant failure and patient morbidity/mortality. CAV etiology is multi-factorial, including promotion by IFN-7 secreting T helper (Th) Type-1 cells (Th1) and the migration/proliferation of smooth muscle cells (SMC) into arterial lumen. The use of rapamycin (RAPA) as an immunosuppressant is associated with reduced CAV, in part through direct inhibition of SMC, but the mechanisms by which RAPA alters the host/graft immunological environment to limit CAV are unclear. We have made the novel observation that prolonged dendritic cell (DC) exposure to RAPA confers DC resistance to pro-inflammatory stimuli by upregulating the transmembrane form of the IL-1R family member ST2 (ST2L). In addition to negatively regulating TLR and CD40 signaling, ST2L is the receptor for IL-33, a cytokine that promotes Th Type-2 (Th2) responses. IL-33 can be produced by a variety of cells, including endothelial cells (EC) and SMC, and may have cardioprotective properties. When the function of IL-33 is blocked, or ST2L is absent, pathology is exacerbated in both atherosclerosis and cardiac hypertrophy models. However, if IL-33 exhorts a Th polarization capacity through direct influence on DC, or can inhibit CAV is not known. Our central hypothesis is that IL-33 promotes DC. especially RAPA-DC expressing increased ST2L, Th2 cell polarization capacity and will prevent CAV bv both inducing Th2 skewing of T cell populations and direct cardioprotective effects on the allograft. In AIM I, we hypothesize that IL-33 induces gene expression arid signaling pathways that mediate a DC capacity to promote Th2 response in vitro and in vivo. In AIM II, we hypothesize that post-operative IL-33 and RAPA alone or, combined with therapeutic DC administration, leads to rejection-free heart allograft survival and prevents CAV by modulating the host immune system towards Th2 and regulatory T cell responses. In AIM III we hypothesize that IL-33 acts via ST2L on both immune cells and cardiac allograft cells to protect cardiac allografts during acute and chronic rejection.